I lean heavily towards the builder, not the cartridge, being the primary source for accuracy. All things equal, most shooters will struggle to shoot the difference in case designs. Reloaders tend to have a bit more say on how easy it is to find accurate loads for particular cartridges, and my experience with the PRC shows it is pretty easy to get to shoot a variety of projectiles. Coupled with good factory ammo (with generally good availability), great brass selection, and the wide variety of 6.5 bullets, I would have to be very, very heavily swayed to choose 6.8 Western over 6.5 PRC.